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Protractors

Surveying

Since the first protractors appeared near the turn of the 17th century, around the same time that the technique of triangulation was developed for surveying, their utility for this activity appeared evident from early on. Surveyors typically carried at least one protractor in their field kits. The instrument might be combined with another drawing instrument, such as a set of parallel rules. By the 19th century, makers tried to blend convenience with multi-functionality, offering rectangular protractors that fit easily in a case or pocket and that were packed with aids for reducing real-world distances to proportional scales. They also showed off their improving craftsmanship with fine objects that retained accuracy in measurement. (See also the page on Engineering & Drafting.)

This steel semicircular protractor is divided by half-degrees and is marked by tens from 360 to 180 and from 180 to 0, both in the counterclockwise direction. A 3/8" line is engraved at the origin point. On its left side, the protractor slides along a steel bar or straight edge. Two thumbscrews at the top of the protractor hold in place a removable scale, which is divided into units of four and marked by 40s from 0 to 720. Forty units correspond to approximately one centimeter. The bottom of each screw is marked "2." The scale moves approximately 60 units to the left or right by turning a third screw against a serrated edge on the scale.

An additional scale accompanies the object. This scale is divided by fifties and marked by thousands from 0 to 12,000. Ten units correspond to approximately 1.5 centimeters. The protractor was originally stored in a mahogany case, apparently discarded by 1959. The protractor was purchased by the U.S. Geological Survey between 1879 and 1907.

According to the accession record, this "special protractor and scale" is attributed to the factory operated by William and Lewis Ephraim Gurley in Troy, N.Y. No examples of this protractor could be identified in Gurley catalogs, although the "special" may refer to a special order placed by the U.S. Geological Survey, which in 1907 declared this instrument "obsolete" and transferred it to the Smithsonian.

This semicircular steel protractor within a rectangular frame is exactly like ID number MA*247967, except that there is no second scale to replace the sliding scale screwed to the top of the protractor. The number 1 is marked on the bottom of each of these two screws. This instrument also retains the bottom half of its original mahogany case, which is lined with blue velvet and bears two brass hooks for latching the case. The protractor is disassembled from the straight edge on which it slides so that both pieces fit in the case.

Reference: Deborah J. Warner, "Browse by Maker: Gurley," National Museum of American History Physical Sciences Collection: Surveying and Geodesy, http://americanhistory.si.edu/collections/surveying/maker.cfm?makerid=14.